Paulo J. A. Ribeiro-Claro

USE OF FTIR, FT-RAMAN AND 13C-NMR SPECTROSCOPY FOR IDENTIFICATION OF SOME SEAWEED PHYCOCOLLOIDS

Many seaweeds produce phycocolloids, stored in the cell wall. Members of the Rhodophyceae produce polysaccharides the main components of which are galactose (galactans)-agar and carrageenan. In addition, alginic acid is extracted from members of the Phaeophyceae. This is a binary polyuronide made up of mannuronic acid and guluronic acid. The wide uses of these phycocolloids are based on their gelling, viscosifying and emulsifying properties, which generate an increasing commercial and scientific interest. In this work, the FTIR and FT-RAMAN spectra of carrageenan and agar, obtained by alkaline extraction from different seaweeds (e.g. Mastocarpus stellatus, Chondrus crispus, Calliblepharis jubata, Chondracanthus acicularis, Chondracanthus teedei and Gracilaria gracilis), were recorded in order to identify the type of phycocolloid produced. The spectra of commercial carrageenan, alginic acid and agar samples (SIGMA and TAAB laboratories) were used as references. Special emphasis was given to the 500-1500 cm(-1) region, which presents several vibrational modes, sensitive to the type of polysaccharide and to the type of glycosidic linkage. The FT-Raman spectra present a higher resolution than FTIR spectra, this allowing the identification of a larger number of characteristic bands. In some cases, phycocolloids can be identified by FT-Raman spectroscopy alone.

Structural and Photoluminescence Studies of a Europium(III) Tetrakis(β-diketonate) Complex with Tetrabutylammonium, Imidazolium, Pyridinium and Silica-Supported Imidazolium Counterions

Tetrakis(naphthoyltrifluoroacetonato)lanthanate(III) complexes (Ln = Eu, Gd) containing the cations tetrabutylammonium, [NBu(4)](+); 1-butyl-3-methylimidazolium, [C(4)mim](+); and 1-butyl-3-methylpyridinium, [C(4)mpyr](+), have been prepared and structurally characterized by single-crystal X-ray diffraction. The {EuO(8)} coordination sphere in [NBu(4)][Eu(NTA)(4)] is best described as a distorted dodecahedron, where the metal ion is located at the 4-fold inversion axis with only one crystallographically independent NTA residue. In [C(4)mim][Eu(NTA)(4)] and [C(4)mpyr][Gd(NTA)(4)], the central Ln(3+) ions are coordinated by eight oxygen atoms from four distinct beta-diketonate ligands, in an overall distorted square-antiprismatic geometry. Besides electrostatic interactions, the crystal packing in all three structures is stabilized by offset pi-pi interactions involving the naphthyl rings of neighboring complexes (and, for [C(4)mim][Eu(NTA)(4)] and [C(4)mpyr][Gd(NTA)(4)], neighboring naphthyl/imidazolium and naphthyl/pyridinium rings) and C-H...pi contacts. The photoluminescence properties of the three Eu(III) complexes were studied at room temperature and -259 degrees C by measuring emission and excitation spectra, (5)D(0) emission decay curves, and absolute emission quantum yields. Under ligand excitation (lambda(ex) = 290-395 nm), the quantum yields (room temperature) were in the range 0.72-0.77 for the 1-butyl-3-methylimidazolium salt. An immobilized analogue of this complex was prepared by supporting [Eu(NTA)(4)](-) on an ordered mesoporous silica derivatized with 1-propyl-3-methylimidazolium groups. The disappearance of the intra-4f(6) lines in the excitation spectrum of the supported material indicated an increase in the ligands sensitization process of the Eu(3+) ions, relative to direct intra-4f(6) excitation. The emission quantum yield measured for the supported material (0.32-0.40, for excitations between 265 and 360 nm) is the highest so far reported for lanthanide-containing ordered mesoporous silicas.

Analysis by Vibrational Spectroscopy of Seaweed Polysaccharides with Potential Use in Food, Pharmaceutical, and Cosmetic Industries

Polysaccharides present in several seaweeds (Kappaphycus alvarezii, Calliblepharis jubata, and Chondrus crispus—Gigartinales, Rhodophyta; Gelidium corneum and Pterocladiella capillacea—Gelidiales, Rhodophyta; Laurencia obtusa—Ceramiales, Rhodophyta; Himanthalia elongata, Undaria pinnatifida, Saccorhiza polyschides, Sargassum vulgare, and Padina pavonica—Phaeophyceae, Ochrophyta) are analyzed by spectroscopic techniques. The nature of the polysaccharides (with extraction and without any type of extraction) present in these seaweeds was determined with FTIR-ATR and FT-Raman analysis of extracted phycocolloids and ground dry seaweed.

The solid-liquid phase diagrams of binary mixtures of consecutive, even saturated fatty acids

For the first time, the solid-liquid phase diagrams of five binary mixtures of saturated fatty acids are here presented. These mixtures are formed of caprylic acid (C(8:0))+capric acid (C(10:0)), capric acid (C(10:0))+lauric acid (C(12:0)), lauric acid (C(12:0))+myristic acid (C(14:0)), myristic acid (C(14:0))+palmitic acid (C(16:0)) and palmitic acid (C(16:0))+stearic acid (C(18:0)). The information used in these phase diagrams was obtained by differential scanning calorimetry (DSC), X-ray diffraction (XRD), FT-Raman spectrometry and polarized light microscopy, aiming at a complete understanding of the phase diagrams of the fatty acid mixtures. All of the phase diagrams reported here presented the same global behavior and it was shown that this was far more complex than previously imagined. They presented not only peritectic and eutectic reactions, but also metatectic reactions, due to solid-solid phase transitions common in fatty acids and regions of solid solution not previously reported. This work contributes to the elucidation of the phase behavior of these important biochemical molecules, with implications in various industrial applications.

Chemistry and Catalytic Activity of Molybdenum(VI)-Pyrazolylpyridine Complexes in Olefin Epoxidation. Crystal Structures of Monomeric Dioxo, Dioxo-μ-oxo, and Oxodiperoxo Derivatives

The dioxomolybdenum(VI) complexes [MoO2Cl2(PzPy)] (1) and [MoO2(OSiPh3)2(PzPy)] (5) (PzPy = 2-[3(5)-pyrazolyl]pyridine) were synthesized and characterized by vibrational spectroscopy, with assignments being supported by DFT calculations. Complex 5 was additionally characterized by single crystal X-ray diffraction. Recrystallization of 1 under different conditions originated crystal structures containing either the mononuclear [MoO2Cl2(PzPy)] complex co-crystallized with 2-[3(5)-pyrazolyl]pyridinium chloride, binuclear [Mo2O4(μ2-O)Cl2(PzPy)2] complexes, or the oxodiperoxomolybdenum(VI) complex [MoO(O2)2Cl(PzPyH)], in which a 2-[3(5)-pyrazolyl]pyridinium cation weakly interacts with the Mo(VI) center via a pyrazolyl N-atom. The crystal packing in the different structures is mediated by a variety of supramolecular interactions: hydrogen bonding involving the pyridinium and/or pyrazolyl N-H groups, weak CH · · · O and CH · · · π contacts, and strong π-π stacking. Complexes 1 and 5 are moderately active catalysts for the epoxidation of cis-cyclooctene at 55 °C using tert-butylhydroperoxide as oxidant, giving 1,2-epoxycyclooctane as the only reaction product. Insoluble materials were recovered at the end of the first catalytic runs and characterized by IR spectroscopy, elemental analysis, scanning electron microscopy (SEM)-energy dispersive spectroscopy (EDS), and powder X-ray diffraction. For complex 5 the loss of the triphenylsiloxy ligands during the catalytic run resulted in the formation of a tetranuclear complex, [Mo4O8(μ2-O)4(PzPy)4]. The recovered solids could be used as efficient heterogeneous catalysts for the epoxidation of cyclooctene, showing no loss of catalytic performance between successive catalytic runs.

C-H...O bonded dimers in 2-methoxy-benzaldehyde studied by X-ray crystallography, vibrational spectroscopy, and ab initio calculations

The crystal structure of 2-methoxy-benzaldehyde reveals the presence of several intra- and intermolecular C–H ��� O short contacts, the strongest one forming a dimer linked by the C@O and C(3)–H groups of adjacent molecules.In the liquid state, the occurrence of a dimerisation equilibrium is concluded from a splitting in the carbonyl stretching mode. The structure of the possible C–H ��� O interactions has been evaluated by B3LYP/6-31G* ab initio calculations. Analysis of the mC–H region allows the experimental identification of a blue shift of the relevant C–H stretching mode in both the solid and liquid phases. 2002 Published by Elsevier Science B.V.

Experimental and Theoretical Evidence of CH⋅⋅⋅O Hydrogen Bonding in Liquid 4-Fluorobenzaldehyde

The presence of C-H...O hydrogen bonds in liquid 4-fluorobenzaldehyde has been studied by a combination of theoretical and spectroscopic methods. Ab initio calculations yielded bond energies and preferred bonding geometries, and the calculated spectroscopic properties have been compared with the experimental results. The presence of C-H...O hydrogen bonds in the liquid phase is strongly supported by vibrational and NMR spectroscopic data. Particular attention is paid to the spectroscopic effects related to the predicted shortening of the C-H bond engaged in the C-H...O contact. The concentration-dependent intensity in the C-H stretching region is tentatively assigned to a blue-shift effect due to C-H...O hydrogen bonding.

Engineering highly efficient Eu(III)-based tri-ureasil hybrids toward luminescent solar concentrators

Following a computational-experimental approach, a highly luminescent β-diketonate-europium(III) complex containing 2-thenoyltrifluoracetonate (tta−) and 5,6-epoxy-5,6-dihydro-[1,10] phenanthroline (ephen) ligands, Eu(tta)3ephen (II), was theoretically studied by DFT/TD-DFT calculations, synthesized from Eu(tta)3(H2O)2(I) and fully characterized by high resolution mass spectrometry, TGA analysis, vibrational, UV-Vis and photoluminescence spectroscopy. For intramolecular energy transfer analysis purpose, Ln(NO3)3(ephen)2 [Ln = Eu (III), Gd (IV)] complexes were also synthesized and complexes I and III were theoretically studied. The organic–inorganic tri-ureasil matrix was used as a support for the immobilization of complex II and two hybrid samples were synthesized as a monolith (MtU5Eu-II) and as a thin film (FtU5Eu-II), characterized and its photoluminescence properties were compared with those of complex II. The photophysical properties of complex II benefit from the synergy between the excited-states of both ligands that create efficient energy transfer pathways to optimize the Eu3+ sensitization contributing to the large emission quantum yield (82 ± 8%), which is one of the highest so far reported for solid lanthanide β-diketonate complexes. Moreover, although the incorporation of complex II into the hybrid matrix is disadvantageous from the quantum yield point of view, MtU5Eu-II and FtU5Eu-II exhibit the highest emission quantum yields reported so far for Eu3+-containing hybrids (63 ± 6% and 48 ± 5%, respectively). Additionally, a significant improvement in the photostability under UV irradiation of the incorporated complex II is observed. The possibility of FtU5Eu-II to be used as a luminescent solar concentrator was evaluated and an optical conversion efficiency of ∼9% as well as an ability to boost up the Si-photovoltaic cell output to 0.5% were verified.

A comparative analysis of phycocolloids produced by underutilized versus industrially utilized carrageenophytes (Gigartinales, Rhodophyta)

Carrageenan (E-407) and semi-refined carrageenan (E-407a) are some of the main additives used by the food industry for their gelling, emulsifying, thickening, and stabilizing properties. These are natural ingredients, which have been used for decades in food applications and are generally regarded as safe. Internationally, sub-tropical carrageenophytes (e.g., Kappaphycus alvarezii) are cultivated extensively as a source of raw materials for industrial extraction, and their use as potential candidates in integrated multitrophic aquaculture is tentative. We analyzed carrageenan yield (as a percentage of dry weight) and chemical composition (by Fourier transform infrared attenuated total reflection and Fourier transform-Raman) of extracts produced by several carrageenophytes (Gigartinales, Rhodophyta), from different origins, e.g., K. alvarezii (Tanzania, Indonesia, the Philippines, Panama, and Mexico), Kappaphycus striatum (Madagascar), Eucheuma denticulatum (Tanzania, the Philippines, and Madagascar), Betaphycus gelatinum (the Philippines), Chondracanthus chamissoi, and Sarcothalia crispata (Chile). For comparison, some underutilized carrageenophytes were also analyzed, e.g., Chondrus crispus, Mastocarpus stellatus, Gigartina pistillata, Chondracanthus teedei var. lusitanicus, Chondracanthus acicularis, Calliblepharis jubata, Gymnogongrus crenulatus, and Ahnfeltiopsis devoniensis (Portuguese carrageenophytes). The main findings were that the highest carrageenan yield was obtained from K. striatum (Madagascar) with 75.6 (percent dry weight (% DW)); B. gelatinum and K. alvarezii (both from the Philippines) had yields of 71.0% and 68.0% (% DW), respectively; and G. pistillata (Portugal) 65.4% (% DW). Spectroscopic analysis of the phycocolloids allowed determination of a wide range of carrageenan types, e.g., pure iota carrageenan, several kappa–iota hybrid carrageenans with different iota/kappa ratios, and kappa–beta, xi–theta, and xi–lambda hybrid carrageenans.

Effect of the Cation on the Interactions between Alkyl Methyl Imidazolium Chloride Ionic Liquids and Water

A systematic study of the interactions between water and alkyl methyl imidazolium chloride ionic liquids at 298.2 K, based on activity coefficients estimated from water activity measurements in the entire solubility range, is presented. The results show that the activity coefficients of water in the studied ILs are controlled by the hydrophilicity of the cation and the cation-anion interaction. To achieve a deeper understanding on the interactions between water and the ILs, COSMO-RS and FTIR spectroscopy were also applied. COSMO-RS was used to predict the activity coefficient of water in the studied ionic liquids along with the excess enthalpies, suggesting the formation of complexes between three molecules of water and one IL molecule. On the basis of quantum-chemical calculations, it is found that cation-anion interaction plays an important role upon the ability of the IL anion to interact with water. The changes in the peak positions/band areas of OH vibrational modes of water as a function of IL concentration were investigated, and the impact of the cation on the hydrogen-bonding network of water is identified and discussed.